Gene therapy for cancer has been studied for a long time, and clinical researches have actually been initiated. Furthermore, RNA-based therapeutic techniques using antisense techniques or ribozyme techniques are being developed.
Attention has been paid to RNA interference (RNAi) in Caenorhabditis elegans, which was reported in 1998, as a phenomenon in which gene expression is suppressed due to sequence-specific mRNA degradation caused by a double-stranded RNA (see, for example, Non-patent Document 1). It is considered that the RNA interference is caused by a mechanism in which a long double-stranded RNA is degraded by an RNase III-type activity called Dicer into a short RNA of 21 to 25 nucleotides called an siRNA (short interfering RNA), and the siRNA is then incorporated into a ribonucleic acid-protein complex called RISC (RNA-induced silencing complex), which binds to a target RNA in an ATP-dependent manner to degrade the target RNA (see, for example, Non-patent Documents 2 to 7). Thereafter, it has been reported that it is possible to suppress gene expression applying the RNA interference also in a mammalian cell (see, for example, Non-patent Documents 8 and 9). Regarding gene expression control using the RNA interference (knockdown), although there are many reports in which expression of a gene transferred from the outside is controlled, there have been few reports in which expression of an endogenous gene expressed in the steady state is knocked down.
α1,6-Fucosyltransferase (GDP-L-Fuc:N-acetyl-β-D-glucosaminide α1,6-fucosyltransferase; FUT8) is a glycosyltransferase that is involved in biosynthesis of an N-linked sugar chain of a glycoprotein, and catalyzes a reaction of attaching fucose to the 6-position of an N-acetylglucosamine residue linked to asparagine in an N-linked complex-type sugar chain. Mouse and human FUT8-encoding genes have been isolated, and the nucleotide sequences have been determined (Non-patent Documents 10 and 11). A cell in which the gene for FUT8 is knocked out for modifying sugar chain modification of an antibody has been produced (Patent Document 1). Furthermore, there is report on knockdown of a gene for FUT8 for a similar purpose (Non-patent Document 12) although the efficiency of suppressing FUT8 expression is low (56 to 65%).
α-Fetoprotein (AFP) is a glycoprotein that is produced in liver. Although it is secreted into serum at embryonic stage, it is hardly detected in serum of a healthy adult. However, the serum APF level is elevated even in an adult if the adult suffers from a hepatic disease such as hepatitis or hepatic cancer. It is known that the amount of AFP to which fucose is attached by the action of FUT8 (called AFP L3 fraction) is increased in a patient with hepatocellular carcinoma. Thus, the AFP L3 fraction is used as a marker for hepatocellular carcinoma. However, the relationship between FUT8 and hepatic cancer is not simple, the activity of FUT8 in serum of a patient with hepatic cancer is not necessarily higher than that of a healthy person, and it is considered that production of glycoproteins having attached fucose in serum, which is known to be increased in a patient with hepatic cancer, requires not only FUT8 but also cooperation with another enzyme or the like (Non-patent Document 13). To date, there has been no finding that control of FUT8 expression is effective in treating a disease.
Patent Document 1: JP-A 2005-224240
Non-patent Document 1: Nature, 391:806-811 (1998)
Non-patent Document 2: Nature, 409:363-366 (2001)
Non-patent Document 3: Genes and Development, 13:3191-3197 (1999)
Non-patent Document 4: Cell, 101:25-33 (2000)
Non-patent Document 5: Cell, 107:309-321 (2001)
Non-patent Document 6: Genes and Development, 15:188-200 (2001)
Non-patent Document 7: Cell, 107:297-307 (2001)
Non-patent Document 8: Nature, 411:494-498 (2001)
Non-patent Document 9: Proc. Natl. Acad. Sci. USA, 98:9742-9747 (2001)
Non-patent Document 10: DNA Sequence, 11:90-96 (2000)
Non-patent Document 11: J. Biochem., 121:626-632 (1997)
Non-patent Document 12: Biotechnol. Bioeng., 88:901-908 (2004)
Non-patent Document 13: Cancer Research, 63:6282-6289 (2003)